1. Field of the Invention
The present invention relates to a belt used for transfer, i.e., a transfer belt such as a transfer material transport belt or an intermediate transfer belt, used in image forming apparatus such as electrophotographic apparatus. The present invention also relates to an image forming apparatus having the transfer belt.
2. Related Background Art
As conventional image forming apparatus, image forming apparatus (electrophotographic apparatus) are well known which employ such an electrophotographic system as described below.
First, the surface of an electrophotographic photosensitive member as an image bearing member is charged, and this surface is then irradiated with exposure light (image exposure light) to form an electrostatic latent image on the surface of the electrophotographic photosensitive member. Next, the electrostatic latent image is developed with a toner to form a toner image on the surface of the electrophotographic photosensitive member, and then the toner image is transferred to a transfer material toner image is transferred to the transfer material, the transfer material is transported by a transfer material transport belt to the position of transfer.
As a system by which the toner image held on the surface of the electrophotographic photosensitive member is transferred to the transfer material, an intermediate transfer system is also well known in which the toner image held on the surface of the electrophotographic photosensitive member is primarily transferred to the surface of an intermediate transfer belt and the toner image on the surface of the intermediate transfer belt is further secondarily transferred to the transfer material.
In the image forming apparatus using transfer belts such as the transfer material transport belt and the intermediate transfer belt, as a method by which the density and position of toner images are detected, a method is employed in some cases in which toner patches are formed on the surface of the transfer belt and the toner patches are detected with a photosensor. This method utilizes the reflection of light from the surface of the transfer belt, and hence the surface of the transfer belt is required to have a high light reflectance.
In the case where this detection method is employed, cleaning (belt cleaning) is required by toner such as the toner scattered when the toner patches are formed are removed from the transfer belt.
Inasmuch as it is advantageous that it is unnecessary to separately prepare any of the members for belt cleaning, in the cleaning of the transfer material transport belt, a method is largely employed in which the residual toner is transferred from the transfer material transport belt to the electrophotographic photosensitive member and then collected in a residual-toner container for the electrophotographic photosensitive member.
In this belt cleaning method, in many cases the transfer material transport belt and the electrophotographic photosensitive member are rotated allowing their peripheral speeds to differ from each other so as to improve cleaning efficiency. However, if the transfer material transport belt and the electrophotographic photosensitive member come into close contact with each other so as to produce a great difference between the static friction coefficient and the dynamic friction coefficient, stick-slip may occur to destabilizing the rotation of, and contact between, the transfer material transport belt and the electrophotographic photosensitive member, so that the cleaning efficiency is not improved. belt, it is also necessary to remove, in addition to the above residual toner, the remaining toner that was not transferred at the time of secondary transfer (secondary transfer residual toner). Accordingly, a method is largely employed in which the toner remaining on the intermediate transfer belt is scraped off and removed with a blade.
In this belt cleaning method, if the intermediate transfer belt and the blade come into close contact with each other, stick-slip may occur or the blade may turn over, thereby lowering cleaning efficiency.
That is, there is a requirement that the surface of the transfer belt, which includes the transfer material transport belt and the intermediate transfer belt, must have friction characteristics and close-contact properties which should be held within preferable ranges.
To resolve this problem, e.g., Japanese Patent Application Laid-open No. H08-202064 discloses a technique in which resin particles of fluorine resin, silicone resin or the like are incorporated into the transfer belt. Also, Japanese Patent Application Laid-open No. 2002-287528 discloses a transfer belt whose friction coefficient and surface roughness are specified. control the transfer belt to have friction coefficient at a certain level or less, it is necessary to use in the surface layer of the transfer belt a resin having small surface energy, or to roughen the surface of the transfer belt.
However, in the above background art, the surface of the transfer belt may have low reflectance when satisfying friction characteristics and close-contact properties. Specifically, since fluorine resin and silicone resin have a low refractive index, the surface of the transfer belt incorporated with any of these tends to have low reflectance. In addition, when incorporating resin particles, voids may occur at the surface of the transfer belt. Such voids cause a lowering of the reflectance of the surface of the transfer belt. Furthermore, if the surface of the transfer belt is roughened, a problem is raised in that diffused reflection increases which is a noise component in the method of detecting the density and position of toner images with a photosensor.